1. Field of the Invention
The present invention relates to a magnetic tape cartridge reel on which a magnetic tape is wound and stored within a magnetic tape cartridge.
2. Description of the Related Art
Conventionally, as a magnetic tape cartridge which has been used as a recording medium for use in external memory such a computer, there is known a magnetic tape cartridge of a type in which a single reel with a magnetic tape is wound thereon. The magnetic tape cartridge is used for storing data of a computer.
As shown in FIG. 6, this type of magnetic tape cartridge 1 is composed in such a manner that a reel 7 consists of a lower flange and an upper flange welded by ultra sonic welding is rotatably stored into a cartridge case 11 composed of an upper case 11a and a lower case 11b fastened together with screws.
The lower flange 3 is made of synthetic resin and is an integral body composed of a cylindrical-shape hub 13 on the outer periphery on which the magnetic tape is wound, and a flange 15 projected in the radial direction of the hub 13 from the lower end outer periphery of the hub 13. On an outer surface of the bottom portion of the hub 13, there is mounted a reel plate 8 to which magnet-type rotation drive means for driving and rotating the reel 7 are connected. Also, in an inner surface of the bottom portion of the hub 13, there is formed a restricting gear 13a which meshes with a restricting gear 32a formed in a brake member 30 so as to restrict the rotation of the reel 7 when it is not in use. Further, in the hub 13, there is formed an opening 13b through which a drive removing spindle which is set in a recording and reproducing apparatus such as external memory using the magnetic tape cartridge 1 can be inserted so as to move the brake member 30 upwardly. Further, around the opening 13b, there is formed a ring-shape groove 13c fitting in the brake member 30.
The brake member 30 has a first member 31 of the cylindrical-shape with a bottom surface and a second member 32 of a cylindrical-shape with a bottom surface in which the restricting gear is formed. On the upper surface of the second member 32, there is formed a cross-shape projection 32b which always meshes with a cross-shape groove (not shown) which is formed in the upper case 11a. 
On the other hand, an upper flange 5 is disc-shape and is welded integrally to the lower flange 3 by ultra sonic welding. In the center of the upper flange 5, there is formed an opening 5a through which an opening edge 13b of the hub 13 is fittingly inserted. As described above, the reel 7 composed of the upper flange 5 and the lower flange welded integrally is biased downward by a reel spring 21 which is attached on the brake member 30 when the reel 7 is stored into the cartridge case 11.
As the magnetic tape cartridge is set to the recording and reproducing apparatus, the meshing engagement of the restriction gear 32a and the restriction gear 13a for restricting the brake member 30 and the hub 13 is released so that the reel 7 can be rotated freely. A magnet-type rotation drive means (winder) connects to the reel plate 8 exposed on the center opening 11c of the lower case 11b. A reader tape 23 is introduced to a predetermined tape traveling pass to be able to record and reproduce date on the magnetic tape 9.
An example of a reel for using in the above magnetic tape cartridge is disclosed in the Japanese patent unexamined publication JP-11-185437-A. Also, in the above magnetic tape cartridge, the magnetic tape is wound on the reel involving in air so called an involved-in air badly affects the rolled posture of the magnetic tape. For example, a technology of preventing this bad influence is disclosed in Japanese patent unexamined publication JP-10-92143-A.
The above-cited JP-10-92143-A discloses, as shown in FIG. 7, on the inner surface of the flange 15, that there are formed a plurality of grooves 15a to release the involved-in air. But there is a problem that enlarging the thickness in the radial direction of the groove 15a to improve the functionality of releasing the involved-in air, causes the width of a convex 33 (a part of contacting magnetic tape) between the adjoining concaves to be decreased. And an edge damage of the magnetic tape 9 becomes remarkable. This is, because the flange 15 forming the reel has high rigidity, in the case when the tape edge contacts with the flange when the magnetic tape is wound on the reel, the edge of the magnetic tape is damaged easily. The conventional reel is composed of the hub 13 and the flange 15 projected in the radial direction of the hub 13 from the lower end outer periphery of the hub 13. In the conventional reel, the hub 13 and the flanges are integrally formed from a synthetic resin, so that it is difficult to make the rigidity of only the flanges 15 themselves low.
Even, when a tape is running, if there is a shifted portion 25 (a step or an undulation) in the direction of the width on the magnetic tape 9 as shown in FIG. 8(a) tape wound body 27 contacts with the flange 15 (or upper flange 5) as shown in FIG. 8(b). As a result, the impact force would concentrate to the shifted portion 25. Accordingly, there easily occurs edge damages such as bending or collapsing. In this case, there is a possibility that some of servomechanism or some of running/recording position detecting systems can not detect the tape edge and the tape can not run.
Also because in the conventional reel 7, the hub 13 and the flange 15 projected in the radial direction of the hub 13 from the lower end outer periphery of the hub 13 are integrally formed, it was difficult to form right angle between the peripheral surface of hub 13 and the flange 13 with high precision, so it needs high technology to make it with high dimensional and shape precision such as the flatness or blur of the plane.